1. Field of the Invention
The invention relates in general to a package structure, and more particularly to a package structure with a heat spreader.
2. Description of the Related Art
As integrated circuit technology changes with each passing day, chips are progressing toward having a high density and a large number of devices. However, a large quantity of heat is generated from the chip in operation. Therefore, a heat spreader is needed to be disposed in the chip in order to release the generated large amount of heat, and thus avoid that the chip is burned down, the circuits have error operation, and the life period of the chip is reduced due to the over-high temperature.
Referring to FIG. 1, a vertical diagram of the substrate without a heat spreader is shown. The substrate 12 has a substrate surface 12a. The ground pad 16 is disposed on the substrate surface 12a, and a die 14 is seated on the substrate 12. Referring to FIG. 2, a vertical diagram of the package structure 10 formed by adhering a heat spreader 20 to the substrate 12 in FIG. 1 is shown. Conventionally, the heat spreader 20 is adhered to the substrate surface 12a by conductive paste. The manufacturing method is performed according to the following steps. First, the conductive paste is formed on the substrate surface 12a and ground pad 16 by adhesive dispensing, and the heat spreader 20 is disposed at a location having the conductive paste on the substrate surface 12a. Afterwards, the heat spreader is adhered to the substrate surface 12a in the paste solidification process, so that the heat spreader 20 can be coupled to the substrate 12 and the ground pad 16. Meanwhile, the heat spreader 20 can be coupled to the ground pad to ground via the conductive paste.
However, when the conductive paste is used to adhere the heat spreader to the substrate surface 12a, the circuit shortcut is resulted very often. Referring to FIG. 3, a cross-sectional view of the conventional package structure along the section line 3—3 in the neighborhood of the ground pad in FIG. 2 is shown. As illustrated in FIG. 3, the substrate 12 has four layers, and substrate solder masks 122 cover the upper and lower surfaces of the substrate 12, excluding the ground pad 16, in order to protect the circuits on the substrate surface 12a. The central layer of the substrate 12 includes a ground layer 18 and a power layer 17. The exposed ground pad 16 contracts with the conductive paste 30 so that the upper surface of the ground pad 16 can be electrically coupled to the heat spreader 20 via the conductive paste 30, and the lower surface of the ground pad 16 can be electrically coupled to the ground layer 18 through the via 182. However, since the heat spreader 20 is coupled to the ground pad 16 by using the conductive paste 30, if some openings 126, such as cracks or crevices, are formed on the substrate solder mask as in the manufacturing process, the circuits on the substrate 12 will have a shortcut to the heat spreader 20 via the conductive paste 30, thereby causing error operations of the die 14.
Conventionally, the heat spreader 20 can also be adhered to the substrate surface 12a by using non-conductive paste. Although, the circuit shortcut issue mentioned above can be solved by this method, however, as the non-conductive paste couples the heat spreader 20 to the ground pad 16, the heat spreader 20 cannot be set to ground via the ground pad 16 due to the non-conductivity of the non-conductive paste. Since the heat spreader is not grounded, its resistance to the electromagnetic interference will be reduced, thereby also easily causing error operations of the die 14.